Photon couplers with solid state lamps

ABSTRACT

A smoke detector with a ribbon of light from a linear array of light emitting diodes directed to an intersection with a ribbonlike path of view of an optically parallel photobar intersecting the light ribbon. A constant current source supplies low current to the diodes.

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Enemark 5] Apr. 10, 1973 [54] PHOTON COUPLERS WITH SOLID [56] References Cited STATE LAMPS UNITED STATES PATENTS [75] Inventor: Robert B. Enemark, Weymouth,

Mass 3,019,346 1/1962 Laycak ..250/219 DF 3,315,176 4/1967 Diard ..250/217 SS [73] Asslgneez Electro Signal Lab, Inc, 3,489,909 1/1970 Martel ..250/219 FR Weymouth, Mass. 3,316,410 4/1967 Meili et a1. ..250/218 [22] Filed: 1972 Primary ExaminerWa.lter Stolwein [21] Appl. No.: 231,659 Attorney-James H. Grover [52] US. Cl. ..250/218, 250/239, 356/207, [57] ABS CT 340/237 A smoke detector with a ribbon of light from a linear [51] 11111. Cl. ..G01n 21/26 array of light emitting diodes directed to an intersec- [58] Field of Search ..250/231, 218, 217 SS; tion with a ribbon-like path of view of an optically parallel photobar intersecting the light ribbon. A constant current source supplies low current to the diodes.

3 Clairrs, 6 Drawing Figures PATENTEDAFRIOIW 3.727. 056

CON STANT CURRENT SUPPLY DET. CIRC.

PHOTON COUPLEIIS WITI-I SOLID STATE LAMPS BACKGROUND OF THE INVENTION Photon couplers requiring a light source and a photodetector include instruments such as smoke detectors whose reliability is dependent upon continued emission from the light source over long periods of time. The recent availability of solid state lamps (SSL) such as the light emitting diode (LED) eliminates one source of failure in smoke detectors and the consequent hazard to lives. Solid state lamps have a life conservatively rated at tens to hundreds of thousands of hours, approaching or exceeding an acceptable ten year life expectancy of an instrument such as a smode detector as compared with the approximately three year life of prior light sources. The SSL is thus particularly well suited for use in smoke detectors and other photon couplers where their life may be considered practically infinite, particularly when operated below rated voltage (General Electric, Solid State Lamps Application Manual, 3-0121, pages 30 and 31).

Notwithstanding the advantage of using a solid state lamp in a photon coupling unit required to be on continuous duty for years, a solid state lamp has the disadvantage in such units of requiring high current to. emit an adequate intensity of light. In a small smoke detector, for example, a typical prior incandescent 360 milliwatt incandescent light source draws 90 milliamperes at 4 bolts D.C. in standby (i.e. no-smoke condition), whereas an SSL with comparable light output draws 0.5 to l ampere at about 2 volts D.C. Such a SSL current drain constitutes over 95 percent of the total requirement of the detection circuit of a typical detector and is a serious economic and market disadvantage, particularly in DC. supplied units.

Accordingly one object of the present invention is to provide a photon coupler utilizing solid state lamps to low currentcurrent drain.

SUMMARY OF THE INVENTION According to the invention a photon coupler comprises a plurality of solid state lamps such as light emitting diodes disposed in an elongate array, a single unitary electric photodetector having a single photoresponsive surface substantially longer than its width, and means supporting the lamp array and photodetector with said photoresponsive surface disposed optically parallel to a substantial portion of the lamp array. Preferably the solid state lamps are connected in series so that their total light output is several times the output of a single large lamp, while the current drawn by the series is a small fraction of the current of a single lamp, the fraction being inversely proportioned to the number of lamps.

DRAWING FIG. 1 is a plan view of a smoke detector according to the invention, shown partly in section;

FIG. 2 is a section on line 2-2 of FIG. I;

FIG. 3 and 4 are plan views of a photodetector and a solid state lamp assembly in the smoke detector of FIG. 11;

FIG. 5 is an enlarged section on line 5-5 of FIG. 4; and

FIG. 6 is a schematic circuit used with the smoke detector of FIG. 1.

DESCRIPTION The insulating block 2 has two internal passages 7.

and 8 of rectangular cross section transversely of the block which open into the chamber 1 along two optical axial planes 9 and 11 at right angles to each other and having an intersection 10. The first passage 7 includes elongate cylindrical cavities Hand 13 and an opening 14! into the dark chamber 1. The second passage 8 includes an elongate cylindrical cavity 16 and an opening 17 into the dark chamber 1. Walls 18 and 19 on opposite sides of the block 2 close the passages and cavities from external light.

In the end cavity 12 of the first passage 7 is a phenolic insulating strip mounting a number, i.e. eight, of light emitting diodes 22, for example, Monsanto type MV50 having a peak spectral emission at 6,500 A. As shown in detail in FIGS. 4 and 5 each diode has two leads 23 fed through the phenolic strip 21 and positioning the diodes in a linear, elongate, closely spaced array extending through the block 2. As shown in broken lines in FIG. 4 and in solid lines in FIG. 6 the diodes are connected in series between two lamp terminals 24. A cylindrical lens 30 of lime glass, for example, directs light from the lamp array in a divergent ribbon extending along the first optical axis 9 into the dark chamber 1 At the end of the second passage 8 is an elongate photodetector having two electrode areas 27 connected to terminals 28 and separated from each other by a zig-zag photoconductive zone 29 too fine in detail to be illustrated. Such a photodetector is available as Allen-Bradley PI-I Photobar, Material C with a spectral response matched to the spectral output of the light emitting diodes. Asecond cylindrical lens 31 enables the photodetector 26 to view the dark chamber 1 along a divergent, ribbon-like path on the axial plane 11 intersecting the light path on the axial plane 9 at The array of diodes 22 and the photodetector 26 are approximately the same length, e.g. 1 inch, and are disposed both physically and optically parallel so that the light ribbon and the ribbon-like viewing path of the photodetector are substantially coextensive at the linear intersection 10. The first cylindrical lens 30 is positioned to focus an image of the lamps approximately at the intersection 10. As is well known in the smoke detection art, smoke and other air-borne particles appearing at the intersection 10 scatter light from the diodes back to the photodetector which responds by a drop of resistance from its value when the chamber is in its normal, dark condition.

, As shown in FIG. 6, the terminals 28 of the photodetector 26 are connected to the input terminals 31 of a detector circuit 32 which senses the resistance drop of the photodetector below a predetermined threshold correlated to smoke density and actuates an alarm or otherwise signals the presence of smoke.

According to the invention an economical and commercially practical low current power source 20 may be used to supply the light emitting diode series. Preferably a constant current supply, the source 20 provides at its positive and negative terminals 25 direct current at 16 volts and 30 milliamperes with a 3 volt drop across a 100 ohm resistor R1 and 13 volts across the series of eight diodes 22. The resistor value is selected to establish a voltage across each of the diodes in the low current portion of its characteristic curve. Such a current drain is comparable to that of prior incandescent light sources yet the eight diode series provides equivalent light output for an infinite time period relative to that of an incandescent lamp. And the standby current of the present diode series in comparison with a single LED of comparable light output is approximately 6 percent, which as previously stated is a decisive factor in the economy of operation and commercial acceptance of a smoke detector.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. Apparatus for detecting fluid borne particles comprising:

means forming a dark chamber substantially excluding light and transmissive of fluid borne particles,

a plurality of solid state lamps mounted in electrical series and an elongate array of predetermined length adjacent the chamber,

a first elongate cylindrical lens disposed parallel to the lamp array between the array and the chamber for projecting a ribbon of light on a path into the chamber,

bar shaped photodetector having a single photoresponsive surface of substantially the same predetermined length as said array mounted adjacent the chamber parallel to the lamp array, second cylindrical lens disposed parallel to the photodetector between the photodetector and the chamber so as to view the chamber on a ribbonlike path having a substantially linear intersection with the ribbon of light, the photodetector being responsive to light modulated by particles at the intersection, and

means for detecting the response of the photodetector to the modulated light.

2. Apparatus according to claim 1 wherein the lamps are connected to a current supply.

3. Apparatus according to claim 2 wherein the lamps have substantially equivalent resistance, thereby to establish substantially equal voltage drops across each diode. 

1. Apparatus for detecting fluid borne particles comprising: means forming a dark chamber substantially excluding light and transmissive of fluid borne particles, a plurality of solid state lamps mounted in electrical series and an elongate array of predetermined length adjacent the chamber, a first elongate cylindrical lens disposed parallel to the lamp array between the array and the chamber for projecting a ribbon of light on a path into the chamber, a bar shaped photodetector having a single photoresponsive surface of substantially the same predetermined length as said array mounted adjacent the chamber parallel to the lamp array, a second cylindrical lens disposed parallel to the photodetector between the photodetector and the chamber so as to view the chamber on a ribbon-like path having a substantially linear intersection with the ribbon of light, the photodetector being responsive to light modulated by particles at the intersection, and means for detecting the response of the photodetector to the modulated light.
 2. Apparatus according to claim 1 wherein the lamps are connected to a current supply.
 3. Apparatus according to claim 2 wherein the lamps have substantially equivalent resistance, thereby to establish substantially equal voltage drops across each diode. 